1. Field of the Invention
The present invention relates to a multimedia broadcast/multicast service (MBMS) and, more particularly, to transmitting and receiving control information for an MBMS.
2. Description of the Related Art
The universal mobile telecommunications system (UMTS) is a third-generation mobile communications system evolving from the global system for mobile communications system (GSM), which is the European standard. The UMTS is aimed at providing enhanced mobile communications services based on the GSM core network and wideband code-division multiple-access technologies.
A related art UMTS network structure 1 is illustrated in FIG. 1. As shown, a mobile terminal, or user equipment (UE) 2 is connected to a core network (CN) 4 through a UMTS terrestrial radio access network (UTRAN) 6. The UTRAN 6 configures, maintains and manages a radio access bearer for communications between the UE 2 and the core network 4 to meet end-to-end quality of service requirements.
The UTRAN 6 includes a plurality of radio network subsystems (RNS) 8, each of which comprises one radio network controller (RNC) 10 for a plurality base stations, or Node Bs 12. The RNC 10 connected to a given base station 12 is the controlling RNC for allocating and managing the common resources provided for any number of UEs 2 operating in one cell. One or more cells exist in one Node B. The controlling RNC 10 controls traffic load, cell congestion, and the acceptance of new radio links. Each Node B 12 may receive an uplink signal from a UE 2 and may transmit a downlink signals to the UE 2. Each Node B 12 serves as an access point enabling a UE 2 to connect to the UTRAN 6, while an RNC 10 serves as an access point for connecting the corresponding Node Bs to the core network 4.
Among the radio network subsystems 8 of the UTRAN 6, the serving RNC 10 is the RNC managing dedicated radio resources for the provision of services to a specific UE 2 and is the access point to the core network 4 for data transfer to the specific UE. All other RNCs 10 connected to the UE 2 are drift RNCs, such that there is only one serving RNC connecting the UE to the core network 4 via the UTRAN 6. The drift RNCs 10 facilitate the routing of user data and allocate codes as common resources.
The interface between the UE 2 and the UTRAN 6 is realized through a radio interface protocol established in accordance with radio access network specifications describing a physical layer (L1), a data link layer (L2) and a network layer (L3) described in, for example 3GPP specifications. These layers are based on the lower three layers of an open system interconnection (OSI) model that is a well-known in communications systems.
A related art architecture of the radio interface protocol is illustrated in FIG. 2. As shown, the radio interface protocol is divided horizontally into the physical layer, the data link layer, and the network layer, and is divided vertically into a user plane for carrying data traffic such as voice signals and Internet protocol packet transmissions and a control plane for carrying control information for the maintenance and management of the interface.
The physical layer (PHY) provides information transfer service to a higher layer and is linked via transport channels to a medium access control (MAC) layer. Data travels between the MAC layer and the physical layer via a transport channel. Also, data transmission is performed through a physical channel between different physical layers, namely, between physical layers of a sending side (transmitter) and a receiving side (transmitter).
The MAC layer of the second layer (L2) provides information transfer service to a higher layer and is linked via a logical channel to a radio link control (RLC) layer. The RLC layer of the second layer (L2) supports the transmission of reliable data and can perform segmentation and concatenation functions for RLC service data units (SDU) received from an upper layer.
The radio resource control (RRC) layer located at the lowest portion of the third layer (L3) is only defined in the control plane and controls transport channels and physical channels with respect to the establishment, re-establishment, and release of radio bearers. A radio bearer (RB) is a service provided by a lower layer, such as the RLC layer or the MAC layer, for transferring data between the UE 2 and the UTRAN 6.
The establishment of an RB determines regulating characteristics of the protocol layer and channel needed to provide a specific service, thereby establishing the parameters and operational methods of the service. When a connection is established to allow transmission between an RRC layer of a specific UE 2 and an RRC layer of the UTRAN 6, the UE 2 is said to be in the RRC-connected state. Without such connection, the UE 2 is in an idle state.
Hereafter, a Multimedia Broadcast/Multicast Service (MBMS or “MBMS service”) will be described. MBMS refers to a method of providing streaming or background services to a plurality of UEs 2 using a downlink-dedicated MBMS radio bearer that utilizes at least one of point-to-multipoint and point-to-point radio bearer. One MBMS service includes one or more sessions and MBMS data is transmitted to the plurality of terminals through the MBMS radio bearer only while the session is ongoing.
As the name implies, an MBMS may be carried out in a broadcast mode or a multicast mode. The broadcast mode is for transmitting multimedia data to all UEs 2 within a broadcast area, for example the domain where the broadcast is available. The multicast mode is for transmitting multimedia data to a specific UE 2 group within a multicast area, for example the domain where the multicast service is available.
The UTRAN 6 provides the MBMS service to the UEs 2 using the RB. RBs used by the UTRAN 6 can be classified as a point-to-point RB or a point-to-multipoint RB. The point-to-point RB is a bi-directional RB, including a logical channel DTCH (Dedicated Traffic Channel), a transport channel DCH (Dedicated Channel) and a physical channel DPCH (Dedicated Physical Channel) or SCCPCH (Secondary Common Control Physical Channel).
The point-to-multipoint RB is a uni-directional downlink RB, including a logical channel MTCH (MBMS Traffic Channel), a transport channel FACH (Forward Access Channel), and the physical channel SCCPCH, as shown in FIG. 3. The logical channel MTCH is configured for each MBMS service provided to one cell and used to transmit user plane data of a specific MBMS service to the UEs 2.
The UTRAN 6 providing the MBMS service transmits MBMS-related control information to the plurality of terminals (UEs 2) through an MCCH (MBMS Control Channel). Herein, the logical channel MCCH is the point-to-multipoint downlink channel and is mapped to the FACH, which is mapped to the SCCPCH. The MBMS-related control information includes a session start for indicating the start of an MBMS service, a session stop for indicating the end of the MBMS service, an RB type indicator for indicating whether the MBMS service is provided via a point-to-point RB or a point-to-multipoint RB, RB information for providing point-to-multipoint RB information such as the MTCH if the RB is a point-to-multipoint RB, counting information for measuring the number of terminals desiring to receive the MBMS service, and re-counting information for re-counting the number of terminals desiring the MBMS service while the MBMS service is being provided.
The MBMS-related control information may be included in an independent message and transmitted, or can be entirely included in one MBMS control message. To transmit various control information related to the MBMS service, the logical channel MCCH is used. Channel mapping of the MCCH is similar to that of the MTCH. Namely, the MCCH is a point-to-multipoint downlink channel and is mapped to the transport channel FACH, which is mapped to the physical channel SCCPCH. For reference, only one MTCH is provided for one service, while only one MCCH is provided for one cell.
The terminal (UE) 2 wishing to receive an MBMS service, must first receive MBMS control information through the MCCH. However, because the terminal 2 can receive only one SCCPCH for the MBMS, and the MCCH is transmitted through a different SCCPCH irrelative to the MTCH, the terminal cannot receive the MCCH if the terminal has already received one or more MBMS services.
An MBMS control information reception indication message (MCCH Indication Message) is used to indicate information to terminals receiving one or more MBMS services, i.e., receiving the MTCH. The MCCH indication message is transmitted through the SCCPCH. The MTCH is also transmitted through the SCCPCH. In order to receive the MBMS data, the mobile terminal 2 receives one SCCPCH. The UTRAN 6 transmits the MCCH indication message through the SCCPCH so that the mobile terminal 2 can receive the control information transmitted through the MCCH. In this case, the MCCH indication message can be transmitted through the MTCH the mobile terminal 2 is receiving, or through an auxiliary channel, such as a Secondary MCCH (S-MCCH), wherein the S-MCCH is mapped to the same SCCPCH as the MTCH. The S-MCCH is an arbitrary channel, which can be a dedicated channel such as a DCCH (Dedicated Control Channel), a common channel such as a CCCH (Common Control Channel), or a new dedicated or common channel. No matter which channel is used, the MCCH indication information is transmitted through the same SCCPCH to which the MTCH is mapped.
The MCCH indication message is a 1-bit indication message. When certain control information is transmitted through the MCCH, the MCCH indication message is used to indicate that the mobile terminal 2 should receive the control information. Namely, when the mobile terminal 2 receives the MCCH indication message in the course of receiving the MTCH, the mobile terminal 2 switches the channel from the SCCPCH through which the MTCH is transmitted to the SCCPCH through which the MCCH is transmitted, and receives the MBMS control information transmitted through the MCCH. After the mobile terminal 2 receives the desired MBMS control information through the MCCH, the mobile terminal 2 then switches the SCCPCH to which the MTCH is mapped and receives the MTCH.
In the related art MCCH indication message, the 1-bit indication message only indicates to the mobile terminal 2 to receive the MCCH. This method is advantageous in that the transmission amount of the indication message can be maximized. However, the related art MCCH indication message also has the following problems. First, the mobile terminal 2 does not know which service the MCCH indication message indicates to receive. Thus, the mobile terminal 2 may receive an MCCH indication message unnecessarily even when control information for a service the mobile terminal 2 does not want to receive is transmitted.
Additionally, the mobile terminal 2 does not know which control information the MCCH indication message indicates to receive. Thus, when various types of control information are continuously transmitted, the mobile terminal 2 does not know which control information to receive, and further does not know at which time the MTCH should be received again. Moreover, if the same control information is transmitted repeatedly several times, the mobile terminal 2 will unnecessarily receive the already-received control message again.
Therefore, in the related art, the mobile terminal 2 frequently receives the MCCH unnecessarily. This is problematic because while the mobile terminal 2 receives the MCCH, it cannot receive the MTCH. Hence, MBMS data is lost. Accordingly, as the mobile terminal 2 reads more MCCHs, the loss of MBMS data increases. A method for minimizing the number of times the MCCH is read by the mobile terminal 2 is therefore required.